1. Field
The present invention relates to communications systems, and more specifically, to systems and techniques for controlling gain of a communications device.
2. Background
Communications systems generally support the exchange of information between two or more communications devices. These communications devices typically include an analog frontend to interface with a communications medium and a digital processor for manipulating the information. Depending on the type of communications device, the analog frontend may be designed with a transmitter, a receiver, or both. The function of the transmitter is to modulate, upconvert, and amplify signals for transmission into free space. The function of the receiver is to detect signals in the presence of noise and interference, and provide amplification, downconversion, and demodulation the detected the signal such that it can be displayed or used by the digital processor.
The receiver typically includes gain control which is commonly referred to in the art as automatic gain control (AGC). One of the purposes of the AGC function in the receiver is to maintain a constant output power over a range of signal input variations. This is typically achieved with an AGC which averages the output power from the receiver and feedbacks this average to the control the gain of the receiver.
In mobile wireless applications, the AGC function may also be employed in the mobile transmitter to prevent a mobile user near a base station from jamming a mobile user that is distant from the base station. The AGC function is performed in the mobile by feeding back the average receiver output power to control the gain of the transmitter in step with the receiver. Thus, if the mobile moves closer to the base station increasing the received power, the AGC will reduce the gain of the receiver and transmitter proportionally. This will result in a proportionally lower mobile transmitter power as the mobile user approaches the base station. This power control technique is often referred to as an open loop control.
The non-linear gain characteristics of the receiver and transmitter may prevent the AGC from operating in an optimal manner. Accordingly, a linearizer is often used in the AGC as a way of compensating for these non-linearities in the receiver and transmitter. A linearizer can be implemented in any number of fashions. One common technique involves the use of a xe2x80x9clook upxe2x80x9d table stored in memory to convert the average receiver power into a gain control signal that compensates for the non-linear gain characteristics of the receiver or transmitter. The contents of the xe2x80x9clook upxe2x80x9d table are determined during a calibration procedure. The calibration procedure generally entails tracking the average power output from the receiver with the AGC loop closed as the input power to the receiver is swept across a specified operating range for different frequency and temperature variations.
To maintain the commercial viability of the communications device, the manufacturer often strives for a simple calibration procedure which reduces the demand on labor resources. Unfortunately, this procedure often dictates a calibration procedure performed over the absolute minimum number of operating frequencies and temperatures that meet the precision requirements of the AGC. The potential drawbacks with a relatively simple calibration procedure become more pronounced with the introduction of multi-media communications devices into the marketplace. By way of example, a multi-media communications device supporting both legacy voice equipment and new data services may require separate calibration procedures for each. Accordingly, there is a need for a communications device that can be supported with a simple calibration procedure that cannot only support different operating frequencies and temperatures, but can also support multi-media modes of operation.
In one aspect of the present invention, a method of gain control includes amplifying a signal with an amplifier having a gain represented by one of a plurality of gain curves depending on a value of a parameter, the signal being amplified at a first one of the parameter values, and controlling the gain of the amplified signal from a predetermined gain curve relating to the gain curve of the amplifier for a second one of the parameter values by adjusting a gain control signal corresponding to a point on the predetermined gain curve as a function of the first one of the parameter values, and applying the adjusted gain control signal to the amplifier.
In another aspect of the present invention, an apparatus includes an amplifier having a gain represented by one of a plurality of gain curves depending on a value of a parameter, and a gain control configured to control the gain of the amplifier from a predetermined gain curve relating to the gain curve of the amplifier for a first one of the parameter values by adjusting a gain control signal corresponding to a point on the predetermined gain curve as a function of a second one of the parameter values, and applying the adjusted gain control signal to the amplifier.
In yet another aspect of the present invention, computer readable media embodies a method of controlling gain of an amplifier having a gain represented by one of a plurality of gain curves depending on a value of a parameter, the method including storing a predetermined gain curve relating to the gain curve of the amplifier for a first one of the parameter values, adjusting a gain control signal corresponding to a point on the predetermined gain curve as a function of a second one of the parameter values, and applying the adjusted gain control signal to the amplifier.
In a further aspect of the present invention, an apparatus includes amplifier means for amplifying a signal, the amplifier means having a gain represented by one of a plurality of gain curves depending on a value of a parameter, and gain control means for controlling the gain of the amplifier from a predetermined gain curve relating to the gain curve of the amplifier means for a first one of the parameter values by adjusting a gain control signal corresponding to a point on the predetermined gain curve as a function of a second one of the parameter values, and applying the adjusted gain control signal to the amplifier.
In yet a further aspect of the present invention, an apparatus includes a receiver having a gain represented by one of a plurality of receiver gain curves depending on a value of a receiver parameter, a transmitter having a gain represented by one of a plurality of transmitter gain curves depending on a value of a transmitter parameter, and a gain control configured to control the gain of the receiver from a predetermined receiver gain curve relating to the receiver gain curve of the receiver for a first one of the receiver parameter values by adjusting a receiver gain control signal corresponding to a point on the predetermined gain curve as a function of a second one of the receiver parameter values, and applying the adjusted receiver gain control signal to the receiver, the gain control further being configured to control the gain of the transmitter from a predetermined transmitter gain curve relating to the transmitter gain curve of the transmitter for a first one of the transmitter parameter values by adjusting a transmitter gain control signal corresponding to a point on the predetermined transmitter gain curve as a function of a second one of the transmitter parameter values, and applying the adjusted transmitter gain control signal to the transmitter.
It is understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein is shown and described only exemplary embodiments of the invention, simply by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.